1. Field of Invention
The present invention relates to a semiconductor device having a weak current channel, in particular a semiconductor device including a weak current channel provided through a first conductive type lightly doped region when the gate of the semiconductor device is in a relatively low voltage range.
2. Description of Related Art
FIGS. 1A and 1B show a prior art semiconductor device 10 which is a double resurf field effect transistor, wherein FIG. 1B is a cross section view according to the cross section line AA′ in FIG. 1A. The semiconductor device 10 includes a substrate SUB and a first conductive type well NW on the substrate SUB. Please refer to FIG. 1B (from left to right), a second conductive type body PBOBY, a source S, an insulation layer FOX, and a drain D are located in the first conductive type well NW. A second conductive type well PTOP is under the insulation layer FOX. The semiconductor device 10 further includes a gate G located above the substrate SUB, a portion of the gate G being on a gate oxide GOX and another portion of the gate G being on the insulation layer FOX.
A control voltage supplied to the gate G controls the current between the source S and drain D, and the current flows through a current channel Ch between the source S and the drain D as shown in FIG. 1B. By the double resurf effect, the current channel Ch has a longer distance, so the semiconductor device 10 is capable of operating under high voltage. However, when the control voltage is in a low voltage range, the conduction resistance is relatively higher, which may possibly cause an operation failure such as off-conduction when the device should be in conduction. Thus, although the semiconductor device 10 can operate under high voltage, it has poor performance in the low voltage range.
Therefore, the present invention provides a semiconductor device to solve the aforementioned problem.